It is proposed to study the mechanism by means of which a recently discovered in vitro enzyme system from Propionibacterium shermanii utilized L-threonine as a source of the 1-amino-2-propanol moiety of corrinoids. In particular the mechanism of L-threonine decarboxylation and the stage of the reaction sequence at which the decarboxylation occurs, as well as the role of ATP, obligatory in the purified system, will be investigated. Studies on NMN deamidase, obtained about 95% pure at the time of writing, will be directed to elucidate the role of a peptide which can be split off from the enzyme under mild conditions and which is needed to restore activity to the residual inactive component. BIBLIOGRAPHIC REFERENCE: Friedmann, H.C. Biosynthesis of Corrinoids, Chapter Two of Cobalamin: Biochemistry and Pathobiology (B. M. Babior, ed.), John Wiley & Sons, Inc., 1975, pp. 75-109.